[Live] Method Name changes in ComponentWithFormTrait + expanded docs

[weaverryan]

Q	A
Bug fix?	no
New feature?	yes (the method name changes)
Tickets	None
License	MIT

Using live components to render a dynamic form is turning out to be a very popular thing to do. The downside is that, in some ways, the form system doesn't "play well" when used so dynamically, which can cause confusion. In this PR:

A) In the docs, I've renamed the property that is bound to your form class to initialFormData to really emphasize that this is the ORIGINAL data used to create the form. It will not represent the new data until the form is submitted. I've also clarified this further in the docs.

B) Updated the docs to talk more about $this->formValues and when data is and isn't updated during the lifecycle.

C) Renamed some methods in ComponentWithFormTrait: getFormInstance() -> getForm() and getForm() -> getFormView(). That's a BC break, and it's going to be annoying... which gives me hesitation. But these are currently named incorrectly (the reason goes back to an old version of live components to help name the variable form in the template).

Cheers!